THE CLASS BIRDS. 311 



is called the keel or brecJiet (b, Fig. 287) ; by multiplying the 

 muscular attachments favourably, it gives more force to the 

 depressor muscles of the wings. 



431. The bones of the shoulder are in like manner 

 favourable for the action of the wings. The scapula (o) is 

 narrow and elongated, and placed in the axis of the spine ; it 

 rests on the sternum not only by the clavicles called four- 

 chette or merrythought (/), but also by the clavicles called 

 coracoid (c), so termed because they seem to be prolongations 

 of the coracoid process in man. The clavicles called fourchette 

 unite generally below with each other, and are attached to the 

 crest of the sternum, and, together with the powerful coracoid 



Fig. 287. Bones of the Shoulder and Sternum, in the Bird.* 



clavicles offer a strong point d'appui for the wings to acton, 

 and these structures are proportioned to the power of flight of 

 the bird. Thus in some of the terrestrial parroquets of Aus- 

 tralia these bones are reduced to an almost rudimentary state,- 

 in the cassowary and American ostrich the fourchette is repre- 

 sented by two small stylets ; in the African ostrich and 

 the tiican they nearly reach the sternum, but do not unite 

 inferiorly ; finally, in some owls they are united inferiorly by 

 cartilage, whilst in the greater number of birds their bony 

 union is complete. In many instances they form a crest at 

 this point of union, and seek a direct support from the 

 sternum. 



The anterior extremities of birds are employed only as 



* s, the sternum ; e, notch of the sternum ; co, origin of the sternal ribs ; 

 b, crest ; f, fourchette ; c, coracoid clavicle ; o, scapula j t, fibrous mem- 

 brane extending from the fourchette to the sternum. 



